1. Field of the Invention
This invention relates generally to strainers which are installed within a pipe coupling. More specifically the invention relates to an apparatus and method for preventing debris, such as small gravel, from being pumped through a pipe coupling connected on one side to a propane gas delivery truck and on the opposite side to a gas storage tank.
2. Description of the Related Art
Gas storage tanks are used extensively to store gas, such as propane, for both residential and commercial use. Once the gas inside of the storage tank has been consumed, or is at least substantially consumed, a gas tank on a delivery truck is connected to the gas storage tank, which then pumps gas into the storage tank to replenish the supply of gas.
FIG. 1 shows a typical prior art system 15 in which a gas delivery truck 24 is shown delivering gas from the truck tank 22 to a permanent gas storage tank 20. In this typical system 15, the gas storage tank 20 connects to a gas intake line 26 that serves as a portion of the gas passage between the truck tank 22 and the storage tank 20. Line 26 typically comprises a stationary metal pipe and has a connector 28 on one downstream end which connects to the gas storage tank 20. The other upstream end of the intake line 26 has a large so-called "Acme" connector 30, exemplified for example by the Acme connector, part number M503-16, which is manufactured by Fisher and Rego, and is, by way of example, used for illustration in the drawings. The phase "Acme connector" is a trade term which refers to a connector having a particular kind of screw thread. It is commonly known in the gas storage tank industry to call connectors with acme type threads "Acme connectors." By way of example, the acme-type threads of Acme connector 30 are shown in FIG. 2 and FIG. 4 at the intake end 60 of Acme connector 30. A back check valve 32 is located in the intake line 26 between the Acme connector 30 and the storage tank 20. The back check valve 32 is commonly known in the art and has a resilient spring that allows the valve to open under pressure and close in the absence of such pressure. When gas is being pumped into the gas tank 20, the pressure from the flowing gas causes the back check valve 32 to open and allow gas to be pumped into the gas storage tank 20. Once gas is no longer being pumped, the pressure from the gas inside of gas tank 20 forces the back check valve into a closed position and stops gas flow out of tank 20.
The gas storage tank 20 also connects to a gas vapor line 40 which is typically a metal pipe of substantially the same length as the intake line 26 but generally smaller in diameter. The vapor line 40 has a connector 42 on one downstream end which connects to the gas storage tank 20. The other upstream end of the gas vapor line 40 has a small Acme connector 44 exemplified by the Acme connector made under part number M-217 by Fisher and Rego, and is, by way of example, used for illustration in the drawings. The vapor line 40 acts to suck gas vapors from the gas storage tank 20 and into the tank 22 on the gas delivery truck 24 when pumping gas into the gas storage tank 20. Gas vapors that remain in the storage tank 20 while pumping gas into the storage tank 20 will exert an opposing force against the gas being pumped into the storage tank 20. Therefore, removing the vapors from the gas storage tank 20 allows the gas to be pumped into the storage tank 20 at a faster rate. An overflow valve 46 is located in the vapor line 40 between the gas storage tank 20 and the small Acme connector 44 to release the overflow of excess gas that might be pumped into the gas storage tank 20.
The gas delivery truck 24 has a discharge hose 48 with a hose coupling connector 31 that through a threaded connection mates to the larger size Acme connector 30 on the intake line 26 for pumping gas from truck tank 22 into the gas storage tank 20. A second hose 50 extends from the gas delivery truck tank 22 and is similarly joined through a hose coupling connector 45 to the smaller size Acme connector 44 on the vapor line 40.
FIG. 2 shows a perspective view of the Acme connector 30 disconnected from the intake line 26 of the gas storage tank 20 and vertically positioned for purpose of illustration with its intake end 60 and exhaust end 62 in upright positions rather than in their normal operational positions as in FIG. 1. The outer threaded intake end 64 of Acme connector 30 releasably mates with the discharge hose coupling connector 31 on the gas discharge hose 48. Gas enters the Acme connector 30 through its intake end 60 and exits through its exhaust end 62. The outside threaded exhaust end 66 of connector 30 releasably mates with a threaded end of the intake pipeline 26 that runs to the gas storage tank 20. A middle portion of the outer surface of the Acme connector 30 forms a hexagonal shape 68 providing flat surfaces for purposes of gripping the Acme connector 30 by means of an appropriate wrench or other tool when installing connector 30 in the pipeline. The intake end 60 of connector 30 includes a first counterbore 70 with a first smooth cylindrical surface of a first uniform internal diameter D-1 (FIG. 4). The first counterbore 70 extends inwardly and terminates substantially in the middle portion of the Acme connector 30 as seen for example in FIG. 4. The exhaust end has a second counterbore 72 which is concentric with but smaller than the first counterbore 70 and forms a second smooth cylindrical surface of a second uniform internal diameter D-2 (FIG. 4). An inwardly sloping planar annular surface 74 (FIG. 4) joins the inner end of the first counterbore 70 to the inner end of the second counterbore 72. FIGS. 2-4 illustrate further details of the Acme connector 30 used by way of example and which will be further described in later description. The Acme connector 30 is typically made of brass.
A common problem with the prior art Acme type connector as has been described above is that small debris such as gravel, bolts, nuts, pump debris and the like will often, for various reasons, accumulate inside of the gas discharge hose 48 before it is attached to the Acme connector 30. For example, the end of the discharge hose 48 might accidentally touch the ground before it is connected to the Acme connector 30, thereby trapping debris inside of the hose 48. Assuming that such small debris is trapped inside of the hose 48 before it is connected to the Acme connector 30, the debris will be pumped towards and most likely into the gas storage tank 20. Once pumping of gas into storage tank 20 commences, such debris can also damage the back check valve 32 and make it inoperable and create potentially hazardous conditions. For example, gravel might lodge in the back check valve 32 while in an open position during pumping of gas into the storage tank 20 and thus prevent the back check valve 32 from closing at the completion of pumping gas into the gas storage tank 20. If the back check valve 32 does not close, then gas from inside of storage tank 20 may leak out into the atmosphere and thus create other potentially dangerous conditions.
Since the later described invention uses a press fitting method, mention is made that it has been known to secure a disc in a connector by press fitting a plug in the connector immediately above the disc as shown in U.S. Pat. No. 4,052,779. However, so far as applicant is aware, it has not been known to provide an annular ring having an outer external surface with both a smooth outer surface portion that loosely but snugly fits into a counterbore within an Acme connector and a knurled outer surface of slightly larger diameter and press fitting the knurled surface of the ring into a tight fit within the connector and using the ring to permanently secure a strainer disc in place within the Acme connector.
An object of the present invention is thus to provide an apparatus and method by means of which the potentially hazardous conditions referred to above can be eliminated.
A more specific object of the invention is to provide an apparatus and method enabling an Acme connector of the type described above to be retrofitted with a permanently fixed strainer located in the path of flow through the connector and in a manner which requires no modification of the connector itself.
Another more specific object of this invention is to provide an annular retainer ring having an outer substantially smooth external surface adjacent a knurled surface of slightly larger diameter and press fitting the knurled portion within a smooth cylindrical surface area of an Acme connector counterbore so as to permanently secure a strainer disc within the connector.
Another object is to provide a method utilizing a setting tool by means of which either of two sizes of retainer rings can be permanently fixed within either of two sizes of Acme connectors.
Other objects will become apparent as the description proceeds.